In modern internal combustion engines, devices for variably adjusting the timing control of gas exchange valves are used to configure the phase relation between crankshaft and camshaft variably between a maximum advance and a maximum retard position within a defined angular range. For this purpose the device is integrated in a drive train via which torque is transmitted from the crankshaft to the camshaft. This drive train may be implemented, for example, as a belt drive, chain drive or gear drive.
The device includes at least two counter-rotatable rotors, one rotor being in driving connection to the crankshaft and the other rotor being connected non-rotatably to the camshaft. The device includes at least one pressure chamber which is subdivided into two counter-working pressure chambers by means of a movable element. The movable element is operatively connected to at least one of the rotors. By supplying pressure medium to the pressure chambers or discharging pressure medium from the pressure chambers, the movable element is displaced within the pressure chamber, whereby a specified rotation of the rotors with respect to one another, and therefore of the camshaft with respect to the crankshaft, is effected.
The inflow of pressure medium to the pressure chambers and the discharge of pressure medium therefrom is controlled by means of a control unit, as a rule a hydraulic directional valve (control valve). The control unit is in turn controlled by means of a controller which determines the actual and reference position of the camshaft relative to the crankshaft (phase relation) with the aid of sensors and compares one to the other. When a difference between the two positions is detected, a signal is transmitted to the control unit which adapts the flows of pressure medium to the pressure chambers to this signal.
In order to ensure the functioning of the device, the pressure in the pressure medium circuit of the internal combustion engine must exceed a given value. Because the pressure medium is as a rule made available by the oil pump of the internal combustion engine and the available pressure therefore rises synchronously with the rotational speed of the internal combustion engine, below a given rotational speed the oil pressure is still too low to change or retain the phase relation of the rotors in a specified manner. This may be the case, for example, during the start phase of the internal combustion engine or during idling phases.
During these phases the device would execute uncontrolled oscillations, leading to increased noise emissions, greater wear, more uneven running and increased raw emissions of the internal combustion engine. In order to prevent this, there may be provided mechanical locking devices which couple the two rotors non-rotatably to one another during the critical operating phases of the internal combustion engine, it being possible to cancel this coupling by charging the locking device with pressure medium. In this case the locking position may be provided at one of the end positions (maximum advance position and maximum retard position) or between the and positions.
A device of this type is known, for example, from U.S. Pat. No. 6,684,835 B2. In this embodiment the device has a vane-cell construction, an outer rotor being mounted rotatably on an inner rotor in the form of a vane wheel. In addition, two rotation angle limiting devices are provided, a first rotation angle limiting device, when in the locked state, allowing the inner rotor to be adjusted with respect to the outer rotor within an interval between a maximum retard position and a defined central position (locking position). The second rotation angle limiting device, when in the locked state, allows the inner rotor to be rotated with respect to the outer rotor within an interval between the central position and the maximum advance position. When both rotation angle limits are in the locked position, the phase relation of the inner rotor to the outer rotor is limited to the central position.
Each of the rotation angle limiting devices consists of a spring-loaded locking pin which is arranged in a receptacle of the outer rotor. Each locking pin is loaded with a force in the direction of the inner rotor by means of a spring. A guide track, which is located opposite the locking pins in certain operating positions of the devices, is formed on the inner rotor. In these operating positions the pins can engage in the guide track. In this case the respective rotation angle limiting device is switched from the unlocked to the locked state. Each of the rotation angle limiting devices can be switched from the locked to the unlocked state by charging the guide track with pressure medium. In this case the pressure medium forces the locking pins back into their receptacles, whereby the mechanical coupling of the inner rotor to the outer rotor is cancelled.
The charging of the pressure chambers and the guide track with pressure medium is effected by means of a control valve, two working ports which communicate with the pressure chambers, and a control port which communicates with the locking groove, being formed, inter alia, on the control valve. Further control valves of this type are known from U.S. Pat. No. 6,779,500 B2. These control valves consist essentially of a conventional 4/3-way directional-proportional control valve which directs the pressure medium flows to and from the pressure chambers, and a 2/2-way directional control valve which controls the flows of pressure medium to and from the rotation angle limiting devices, the part-valves being arranged in series. In this case the two part-valves have a common control piston and a common valve housing.
A disadvantage of these embodiments is the large space requirement of the control valve, above all in the axial direction of the valve housing. In addition, the high number of control structures, which have to be formed on the control piston, is disadvantageous. This entails increased cost and increased space requirement. A further disadvantage is that these control valves are not suited to being used as a central valve which is arranged in a central receptacle of the inner rotor. Firstly, the control valves have two inflow ports to which pressure medium must be supplied via the inner rotor of the device. This increases the complexity and susceptibility to error of the device. Furthermore, the device must be constructed wide in the axial direction in order that all five ports of the valve are covered by the receptacle of the inner rotor. This entails increased cost in manufacturing the device. In addition, the space requirement and weight thereof are increased.